The compounds of the formula (I) of the invention can be considered as analogs of prostacyclin (PGI.sub.2), a physiologically very important natural substance, which are stable and possess a selective pharmacological action.
Prostacyclin (PGI.sub.2) as a metabolite of arachidonic acid, which is wide-spread in mammalian organisms, was discovered in 1976. This substance possesses a number of therapeutically valuable biological effects: e.g. inhibits the aggregation of the blood platelets, lowers the blood pressure, dilatates the airways and diminishes the gastric juice secretion. In addition, prostacyclin shows a cyto-protective action in various organs, e.g. in the stomach, liver, heart and kidney. This means that the destructive consequences of various organ-damaging effects can be prevented or remedied by prostacyclin.
A large number of review articles have been published on the above-mentioned advantageous pharmacologic effects of prostacyclin (see e.g. Flohe et al.: Arnzeimittelforschung 33, 1240 (1983); S. Moncada and J. R. Vane: J. Med. Chem. 23, 591 (1980); W. Bartman et al.: Angewandte Chemie, Int. Ed. Engl. 21, 751 (1982); R. F. Newton et al.: Synthesis 1984, 449).
Today, the advantageous pharmacological actions of prostacyclin are also utilized clinically. The sodium salt has been commercialized by the Wellcome company under the trade name Flolan and by the Upjohn company under the trade name Cycloprostin in 1983 (Drugs of Today 19, 605 (1983)) for cardiopulmonary bypass proceses, perfusion in the course of liver deficiency and kidney haemolysis as areas of indication.
However, severe problems with the use of prostacyclin are induced by the extraordinary unstability of this substance (A. J. Kresge et al.: J. Chem. Soc. Chem. Comm. 1979, 129). The most sensitive moiety of the molecule is the ethanolether functional group. The main principles of the chemical and biological stabilization of the molecule are reported in the above-cited review articles.